(1) Field of the Invention
This invention relates to an aluminum-base bearing alloy and a bearing metal which is made by applying the above bearing alloy to a backing steel by pressure welding. More particularly, the invention relates to an Al-Sn alloy which is prepared by adding tin to aluminum base metal and the bearing alloy of the invention is characterized in that the lowering of its hardness under high temperature conditions is small, the fatigue strength is high and the adhesion thereof to the backing steel is quite large in practical use.
(2) Description of the Prior Art
In the conventional art, Al-Sn alloys have mainly been employed as aluminum bearing alloys. When this kind of alloy is used for the bearings of automobile engines, however, fatigue failure is liable to occur in a short period of time especially when an engine is run at full-load continuously. It is considered to be attributable to the fact that the lubricant oil in an engine becomes too hot during continuous full-load running, for example, the temperature of the oil in the oil pan is raised to 130.degree. C. or higher, so that the lubricant oil on the sliding surface of the bearing becomes considerably high, and accordingly, in the conventional Al-Sn alloy, the hardness at high temperature conditions is suddenly lowered since the eutectic point of such alloy is about 225.degree. C. or so, which reduces the fatigue strength.
Further, in addition to the lowering of the fatigue strength due to the loss of hardness at high temperatures mentioned above, the coarsening of tin particles in the texture of conventional Al-Sn alloy also causes lowering of the fatigue strength. That is, the aluminum bearing material is formed by applying Al-Sn alloy to a backing steel through pressure welding, in which an annealing step is required after the pressure welding in order to improve the adhesive strength between both metals. The annealing is generally done at a temperature below the point at which an Al-Fe inter-metallic compound deposits (about 475.degree. C.) and the higher the treating temperature is and the longer the treating time is, the larger the adhesion strength becomes. As a matter of fact, when the Al-Sn alloy is placed in a high temperature condition during annealing, the migration of aluminum crystal particles and tin particles in the alloy texture is caused to occur and as the result of this, the tin particles become coarse with the passing of time. In brief, when the conventional aluminum bearing alloy is subjected to annealing in order to improve the adhesive strength, the coarsening of tin particles is caused to occur, which results in lowering of the hardness of the Al-Sn alloy at high temperatures. Accordingly, the fatigue strength of the alloy is reduced.